Though most people have an idea of what is and isn't graffiti, a technical definition is difficult to obtain. The word "graffiti" is the plural of "graffito," which is Italian for "little scratch." The World English Dictionary gives the nebulous definition of "drawings, messages, etc, often obscene, scribbled on the walls of public lavatories, advertising posters, etc," whereas Merriam-Webster online identified it as "usually unauthorized writing or drawing on a public surface." In recent years, the word "graffiti" has also been used to refer to the style of painting with spray paint that originated in 1980s New York, regardless of where the painting occurs. To complicate matters further, "street art" is a style of both legal and non-legal art that typically does not follow the standard stylistic rules of the New York "graffiti" style. Because of this lack of definition, determining what is and is not graffiti is a complex and often subjective process.
In order to determine whether a piece of writing or imagery is legal signage or graffiti, each piece must be looked at individually, with special attention paid to certain indicators. Signage that is printed on high-quality materials (such as heavy paper, rubber, tarp, vinyl, porcelain or lighting) is much more likely to be legal signage than graffiti, as these materials are too expensive for most graffiti artists to use. Additionally, if the signage is located in a spot that seems to indicate that it holds a decorative or informative purpose for a business or home, it is likely not graffiti.
Easy indicators of graffiti are the use of spray paint, use of a common graffiti style such as "wildstyle," gang letters or bubble letters, and having a location separate from or in conflict with a business or privately owned space. Graffiti is often done quickly and is frequently found in groupings where various artists have written near each other, so flaws such as paint drips or nearby graffiti can also be indicators. Much of what is considered graffiti does not use a common graffiti painting style, so ask yourself whether the marking in question has any practical purpose, such as denoting a location or name, serving as advertising or providing other common information. If it does not, it is likely graffiti.
Further blurring the line between legal signage and graffiti is the use of graffiti in legal signage. This is common with advertisements and store fronts, which look to capitalize on the popularity of the style. Because of this, the only true way to determine whether something is a legal marking is to ask the owner of the property if he wants the marking there or not.